Solvent extraction process and apparatus



AP 26, 1949. H. R. DAvls SOLVENT EXTRCTION PROCESS AND APPARATUS FiledSept. 6., 1946 www 'fw IN VEN TOR.

'Patented Apr. 26, 1949 soLvEN'r Ex'rnAc'rIoN Pnocrzss AND APPARATUSHyman R. Davis, Jackson Heights, N. Y., assignor to The Lummus Company,New York, N. Y., a

corporation of Delaware Application September 6, 1946, Serial No.695,219

3 Claims. l

This invention relatesto apparatus for, and a method of treating oneliquid countercurrently with another and has particular reference tothe' countercurrent treatment of hydrocarbon oils with a liquid, such asa selective solvent.

This invention broadlycontemplates effecting countercurrent treatment ofliquids in a packed tower, wherein at successive points in the tower theliquid phases are separated, subjected to mixing, preferably cooled, andreturnedtto the tower at or near the point of separation as will be morefully described.

`In the treatment of hydrocarbon oil, -such asA mineral lubricating oil,with a selective solvent, such as furfural', the oil is introduced tothe lower portion ofa packed tower, while the solvent is introduced tothe upper portion thereof. Oil and solvent move countercurrently throughthe tower and in doing soform within the tower the-extract and rafiinatephases. The extract phase is richv in aromatic landnaphthenic typeconstituents of the oil and accumulates in the bottom of the tower, fromwhich it is continuously withdrawn. l

The raifinate phase, o n the other hand, comprises the more parainicrandinsoluble constituents of the oil mixed with a small portion oi thesolvent. This rafiinate phase accumulates in lthe upper portion of thetower and is continuously withdrawn therefrom.

The present invention involves providing, at intervals within the tower,preferably between succeeding sections of packing material, means forseparating the extract and raffinate phase liquid, subjecting it tointimate mixing, and cooling and returning it to the tower.

By these means, close control of the contact between oil and solvent iseffected. The overall effect is to product within the extraction towerconditions somewhat similar to those prevailing in a stage counterflowoperation, as carried out in a series of separate mixing and settlingvessels. v

The purpose of the invention, therefore, is to combine in acountercurrent extraction systemA thev simplicity of operationpermitted' in a conventional packed tower. and the extractive efIlcivency of a stage operation.

Further objects and advantages of my invention will appear from thefollowing description of a preferred form of embodiment thereof taken inconnection with the attached drawing in which:

Fig. l is asubstantially central vertical section with partsdiagrammaticallyshown of the extraction tower.

(Cl. MiG-14.49)

Fig. 2 is a horizontal cross section substantially on the line 2-2 ofFigure 1.

In accordance with my invention the extraction column generallyindicated at I0 is preferably a. vertical cylindrical vessel to whicha'solvent, such as furfural, is introduced through an inlet II to theupper vpart of the tower, while the oil to be treated is introducedthrough an inlet I2 near the bottom. Spraysor spargers or otherdistributing devices I3 and I4 will be provided for the appropriatedistribution of the solvent and the oil through the column. The columnis provided with a screen I5, in the upperpart of the column,forreceiving suitable packing, such as nests of Raschig rings, or othermaterial commonly used as packing, and which has a large surface area ofcontact. The lower portion of the column is similarly provided with ascreen I6 also adapted for supporting a series of packing elementsgenerally indicated at I1.

Withiny the enlarged space between the upper and lower packing sections,I provide a conical baille I8 which extends to the wall of the tower I0and has a central upwardly extending cylindrical neck I9. Such aconstruction provides a chamber 20 which is adapted to catch and retainall liquids flowing downward from the upper portion of the tower.

The conical wall of the baille I8 may be provided with a series ofconduits 22 each leading to a central trap 24 which in turn is providedwith a drawoff pipe 25 so that all of the liquids ilowing downward canbe removed through the pipe 2l. The pipe 25 in turn is connected to pump26 which in addition to drawing oi the liquid also acts as a mixer forthe liquid material which it distributes throughout the cooler 21, andreturns through line 28 to the tower.

The line 28 is connected with a distributing device 29 maintained withinthe central cylindrical neck of the baille I8 in such a manner that allof the liquid previously drawn from' outside of the Ibaille and cooledis now permitted to pass downwardly in spray form within the baille.

The phase liquid collecting in the trough or chamber 20 comprises mainlyextract phase or heavy gravity material rich in solvent and this passesagain countercurrent to the rising liquid that passes upwardthrough thecylindrical neck I9 onvthe baffle I8 and around the baffle 3l whichprevents the solvent from passing directly downward through the tower.

Thus thearrangement of the baille is such, .hat'z upper part of thetower cannot pass directly through the mixed phase portionl to thebottom of the tower.

The cooler 21 eiectively maintains the desired temperature'gradient fromtop to bottom within the tower, the lower portion of the tower adjacentthe oil `feed being at approximately 220 F. and the top of the tower atthe raffinate stream removed at 32 being at approximately 290 F, If itis assumed that the temperature at the liquid drawoff 25 isapproximately 270 F., the liquid can be cooled by the cooler 21 to 240F. thus maintaining a temperature relation in the central part of thetower of 240 F. although the temperature of the liquid itself which iscooled in the trough 20 is 270 F.

It is contemplated that selective solvents other than furfural may beemployed as, for example,

phenol, nitrobenzene', aniline, benzaldehyde, etc.,

and the oil treated may comprise lubricating oil 'stocks or otherpetroleum fractions.

While I have shown a preferred form of embodiment of my invention, I amaware that many modifications and variations may bemade thereto, and I,therefore, do not wish to be limited eX- cept by the scope and spirit ofthe description herein and the claims appended hereto.

I claim:

1. In the countercurrent treatment of hydrocarbon `oil with a solvent toseparate the oil into extract and railnatevphases, the method comprisingpassing the oil downwardly and the solvent upwardly through a packedvertical tower, at vertical intervals throughout the tower segregatingthe oil and solvent into intermediate extract and rafiinate phases,withdrawing at the central part of the tower a segregated relativelywarm intermediate extract phase which is lean in oil and rich insolvent, cooling said withdrawn intermediate extract phase and returningit to an` intermediate portion of the tower in such a manner that thecooled intermediate extract phase A flows downwardly countercurrently tothe oil to increase the strength of the extract phase withv outcontacting the segregated relatively warm intermediate extract phase,and removing the extract phase from the lower part of the tower.

2. In a packed tower for effectingcountercurrent contact between aliquid and a selective solvent, the combination comprising an enlargedby said returned liquid will pass on downward in the towercountercurrent to liquid passing upward through said baiiied trap.

3. A packed tower as claimed in claim 2 in which said trap includes atruncated cone the, l large edge of which forms a liquid reservoir withthe tower, said cone having a central opening and a baille membersurmounting the cone and pre-v venting flow of liquid through the coneto the lower part of the tower, the liquid return means being locatedbelow the baille member and within the opening of the cone.

HYMAN R. DAVIS.

vREFERENCES CITED The following yreferences are of record' in the fileof this patent:

UNITED STATES PATENTS Number Name Date 2,064,422 Fenske et al. Dec. 15,1936 y 2,176,429 Kiersted Oct. 17, 1939 2,216,602 Ragatz Oct. 1, 1940

